Regain Touch Bar "back" functionality of Vscode lost after Touch Bar is gone with Karabiner-Elements (which is actually possible with a hard shortcut of Ctrl+Hyphen) by assigning it to fn key.

karabiner.json

[...]
 "rules": [
      {
          "manipulators": [
              {
                  "conditions": [
                      {
                          "bundle_identifiers": [
                              "^com\\.microsoft\\.VSCode$"
                          ],
                          "type": "frontmost_application_if"
                      }
                  ],
                  "description": "Vscode Ctrl-; goto location",
                  "from": {
                      "key_code": "fn"
                  },
                  "to": [
                      {
                          "key_code": "hyphen",
                          "modifiers": [
                              "left_control"
                          ]
                      }
                  ],
                  "type": "basic"
              }
          ]
      }
  ] 
[...]